Title: Kinematically distinct cores: the unexplained smoking guns of hierarchical galaxy formation
Abstract: The vast majority of galaxies are kinematically boring objects. Stellar motions can be easily predicted from their light distributions implying a majority of galaxies are discs or oblate axisymmetric systems. There are, however, exemptions to the rule. Those galaxies show spectacular kinematic features, the kinematically distinct cores, which are surprising in their appearance, kinematics and dynamical stability. They imply that in some (mostly massive) galaxies the centres have different kinematics from the rest of the galaxy, with angular momentum vectors sometimes misaligned for 90 or even 180 degrees. Since their discovery, the kinematically distinct cores were heralded as evidence of mergers. Still, how are they made, how do they survive and how do host galaxies actually look like internally? These are the questions to which we are still trying to find answers. In this talk, I will present the properties of these fascinating objects, from kinematics and stellar populations point-of-views, and review our changing ideas on their structure and the possible formation scenarios.
Title: Quark stars, quark novae, and how they may relate to gamma-ray bursts
Abstract: Quark stars are hypothetical objects made of deconfined u, d, and s quarks, with masses and radii comparable to neutron stars. They may form if the central density in a neutron star excedes a critical value at which quarks deconfine, which may happen if a rapidly rotating quark star spins down, or if it accretes. The strange quark matter hypothesis states that u-d-s quark matter in bulk may be at a lower energy state than normal nuclear matter. The conversion would release much energy and may happen in an explosive process termed a quark nova. Depending on the conditions surrounding the quark nova, it may lead to interesting observational phenomena. I will discuss how this may explain long gamma-ray bursts.
Title: Very Massive Stars
Abstract: The upper limit to stellar masses is unclear, as is the relative importance of “nature” (stellar physics) and “nurture” (formation environment) to the limit. I will argue that quasar disks may form stars, and that the mass scales there are larger than in giant molecular clouds. This gives cause to look again at the limits imposed by stellar physics. We have studied pulsational instabilities of modern solar-metallicity models up to 938 solar masses. Despite some uncertainties in the linear growth rate, we conclude that these modes saturate non-linearly at small and harmless amplitudes. Vigorous, optically thick winds driven by the Rosseland-mean opacity near 100,000 K are more likely to limit the main-sequence lifetime.
Title: Early-Type Galaxy Stellar Populations in the Near-Infrared
Abstract: Stellar population synthesis (SPS) models are key to interpreting the spectral energy distributions (SEDs) of galaxies. While current models typically agree at optical wavelengths, these same models make vastly different predictions in the near-infrared due to different treatments of late-stage stellar evolution, in particular, the thermally-pulsing asymptotic giant branch (TP-AGB) phase. Models including a large TP-AGB contribution, when applied to the integrated SEDs of intermediate age populations, result in derived ages and masses a factor of two lower than those obtained using models with a lesser TP-AGB contribution. In an effort to resolve this discrepancy, we have tested three popular SPS models, with a focus on evaluating the differing treatments of this phase. We fit the models to high quality near-infrared spectroscopy of a sample of galaxies with well-known spectral properties. In this talk I will present the results of this research.
Title: Star Formation and Galaxy Evolution in Dwarf Galaxies in the Sami Survey
Abstract: Star formation in dwarf galaxies is examined with integral field unit spectroscopy (IFUS) – that spatially resolves each galaxy to provide a spectrum and photometry at many positions across the galaxy. Existing galaxy indices for concentration, asymmetry and clumpiness have been modified for the richer, more informative IFU datasets. It is expected detailed understanding of the distribution of star formation will constrain theories of dwarf galaxy formation and evolution. Some controversies in dwarf astronomy are considered: dwarf galaxies are unimodal in the colour magnitude/mass diagram with no red sequence below log M*= 9; the only differences between dwarf types (such as DEs and DIs) are the SFR and SSFR distribution; and the star formation history is the same for various dwarf types. Star-forming galaxies at high-redshift often display giant kpc-scale clumps that are foci of intense star formation. The blue clumpy structure, asymmetry, and lack of central concentration of these high-z clump cluster galaxies bear a striking resemblance to local dwarf irregulars. Clumps at high redshift are primarily the result of smooth streams of gas flowing onto unstable disks, and not a result of mergers. Simulations reveal clumps interact with each other and the halo, losing angular momentum and spiralling into the centre to build the bulge. The study will consider the role of clumps in dwarf galaxies in galaxy formation and evolution. Star formation in 190 dwarf galaxies in the SAMI IFU survey was measured and the clumpiness fraction determined using the Conselice clumpiness index, the Gini index, and by visual methods. In preliminary results a substantial proportion of SF in dwarf galaxies is not the result of mergers.
Title: The Cosmic Evolution of Neutral Atomic Hydrogen Gas
Abstract: In order to understand the evolution of star formation in galaxies one needs to understand the evolution of neutral atomic hydrogen gas (HI), an important supply of fuel for star formation. In this talk I will outline how neutral atomic hydrogen gas can be measured at a variety of red shifts and present the current status of measurements of the cosmic neutral atomic hydrogen gas density. I will also examine how the neutral atomic hydrogen gas density may vary in different density environments in a way different from the overall cosmic density pattern. Finally I will discuss the likely effect on this area of science of current and future radio telescopes along with future planed surveys.
Title: What are Radio-AGN, how common are they and what are they doing to their host galaxies?
Abstract: Radio-AGN are loud, energetic and boisterous entities usually characterised by their excessive volume in radio-frequencies and the ability to generate large powerful jets, which are often used to hose down their friends and neighbours. Much research has been done into what causes these otherwise normal (if incredibly overweight) black-holes to start acting-out this way, and the impact they have on their surrounding environment. Unfortunately the verdict is still out on whether or not these ‘Radio-AGN’ types have a positive or negative effect on house prices in their neighbourhood, some argue that they bring life and joy to the area via increased star-formation whereas other claim they shut down the galaxy entirely, leaving nothing but groups of old stars pottering around town. Further studies suggest that Radio-AGN tend to prefer larger cities in the form of the most massive galaxies and that these preferences don’t really change as the universe ages. Fortunately for us, the loudest, noisiest and most powerful radio-AGN are rare in the local universe. Unfortunately this means that they are more common at high redshifts and as such, to really see the impact radio-AGN have on their host galaxies optical emissions, we have to observe at infra-red wavelengths to very deep levels [25mag]. We present results of just such a study based on two near-infrared galaxy surveys: ZFOURGE & NMBS, comparing Radio-AGN hosts and non-hosts in term of mass, redshift and star-formation rates. For the results, you will need to come and listen!
Title: Determining the the cosmological sensitivity of next generation radio continuum surveys
Abstract: In the last few years it has become readily apparent that the next generation of radio continuum surveys, planned mainly for the SKA and its pathfinders, are capable of placing significant constraints on the parameters of dark energy and modified gravity. Current plans to achieve these results make use of subtle cosmological effects such as the Integrated Sachs-Wolfe Effect, Cosmic Magnification and the spatial power spectrum to constrain a variety of cosmological models. We present recent work comparing the benefits and drawbacks of applying such cosmological tests to the upcoming Evolutionary Map of the Universe (EMU) survey against those to be carried out on optical/IR cosmology surveys, such as the Dark Energy Survey (DES). While both surveys present predictions of their ability to test basic cosmology in a variety of ways, it is currently difficult to compare these predictions due to the lack of a common framework. As such our comparison of the two surveys in a single unified parameter space allows simple, absolute comparisons between them for the first time, thereby enabling us to predict the significance of the EMU cosmology results.
Title: Opening Real Science: teaching maths and science to reflect authentic practise
Abstract: The Opening Real Science (ORS) project is a Macquarie-led collaboration of several universities and research organisations to infuse real and authentic science into primary and secondary classrooms. The project equips pre- and in-service teachers with ideas and resources designed to showcase science and mathematics as they are practised. The ORS approach is to improve student learning through building teacher confidence and depth of experience. To achieve this, ORS brings together teacher educators and scientists to deliver online teacher education modules and professional experiences designed around inquiry-based learning. The payoffs are significant as ORS partner universities enrol more than a quarter of all Australian education students. The online delivery of modules extends this reach further. In this short talk I will give an overview of ORS and how it is addressing these goals. I will focus on one of the astrophysics modules, Life and Death of Stars, to illustrate design considerations and challenges. I will discuss module structure in the context of both educational theory and classroom practice.
Title: Large scale structure and giant radio galaxy morphology
Abstract: Giant radio galaxies (sizes > 700 kpc) offer a unique opportunity to study the warm-hot intergalactic medium (WHIM), the 10^5 to 10^7 K gas permeating the large scale structure of the present-day universe. The WHIM is thought to harbour significant numbers of baryons — expected from big bang nucleosynthesis — but as yet unaccounted for by observations. In this short talk I will present recent published work from our study of 19 giant radio galaxies and their surrounding environments. We have combined high-sensitivity ATCA radio observations with 10k AAT red shifts to study the relationship between environment, WHIM density and radio lobe morphology. We find that the jets of giant radio galaxies are deflected away from galaxy overdensities and form in directions orthogonal to these. We also find that lobe asymmetries arise when galaxy overdensities occur in the path of one of the jets. Ongoing work extends these observations to density and gravity field reconstructions of each host environment, quantifying the influence of ram pressure on spectral and dynamical age on the radio lobes. When complete, this analysis will offer greater insight into the physical nature of the WHIM across a significant sample size of different environments.
What’s the Matter with Galaxies ?
Abstract: Although it is critical in derivations of galactic parameters (particularly mass), constraints on the Initial Mass Function (IMF) remain uncertain. For my MRes project, I investigate the systematic trend of the IMF that was discovered by the ATLAS3D survey, in attempts to confirm and constrain it. In addition, my work should allow the methodologies used by ATLAS3D to be applied to broader galaxy samples, resulting in tighter IMF constraints in the future. In the talk, I will detail the modelling techniques used by both the survey and myself, as well as some of my very preliminary work.
Title: On the importance of understanding the common envelope phase
Abstract: Many objects and phenomena in the Universe, such as cataclysmic variables and Type Ia supernovae, have short period binaries as their progenitors. Some of these objects are prime candidates for observing gravitational waves with LIGO, while transient phenomena will be seen in great numbers by the LSST (both of which are coming online this year). We now know that compact binaries are formed as a result of a common envelope event, wherein a main sequence star will expand to engulf its companion, with the two stars spiralling close together as orbital angular momentum is transferred to the envelope. While the overall idea of this process is understood, there are still gaps in the knowledge relating to the actual physics involved. It is unclear which progenitor systems lead to compact binaries, and which will end up as mergers. Further, simulations of common envelopes typically end with most of the envelope remaining bound to the system, indicating a lack of understanding of one or more facets of the interaction. In this talk I will discuss these issues, as well as outlining my work with the smoothed particle hydrodynamics (SPH) code, PHANTOM, that will be attempting to resolve some of the issues.
Title: The ZFOURGE survey: the evolution of galaxies since redshift z=4
Abstract: I will review results from the ZFOURGE survey, a new imaging campaign to track galaxy evolution over the last 12 billion years. Deep Magellan near-infrared imaging taken with medium-bandpass filters allows us to finely sample galaxy spectral energy distributions and derive unprecedented photometric red shifts and stellar population parameters at z > 1.5. Using ultra-deep Ks-band imaging (25.5-26 AB mag. 5-sigma) in 3 deep fields (COSMOS, UDS, GOODS-S) to select galaxies, we have constructed large stellar mass-limited galaxy samples to redshift z=4.
With these catalogues we have: (1) conducted an evolutionary study of the star-forming and quiescent galaxy stellar mass functions to a redshift of z=3, (2) demonstrated the existence of quiescent galaxies out to z=4, (3) performed a general census of the massive galaxy population at z=3-4 (4) tracked the evolution of radio, infrared and X-ray active galactic nuclei host galaxies and (5) discovered one of the most distant galaxy clusters known.
Title: Dust Formation in Core-Collapse Supernovae
Abstract: Recent detections of large amounts of dust in high red shift galaxies suggest that core collapse supernovae (CCSNe) may play an important role in the dust budget of the universe. In these high-z galaxies, with ages less than 1 Gyr, there has not been enough time for low-mass AGB stars to form, so much of the dust may come from high-mass stars in SN explosions. For the past decade, we have been following numerous, nearby CCSNe with Gemini, HST, Spitzer, Herschel, and ALMA to look for indications of dust formation, which appear within the first few years of explosion. In particular, I will discuss the recent discovery of a large amount of cold dust associated with SN 1987A. I will discuss these results and their implications for SNe as major dust contributors in the universe.
Title: Producing Robust Ensemble Measurements from the Gaia-ESO Survey
In this talk I will outline the background of the Gaia-ESO Survey, the statistical methods used to combine measurements from many disparate analysis techniques, causal inferences that can be made from these data (e.g., what have we learned from this process), and champion some of the scientific successes from the Survey.
Title: Using GAMA to understand WISE and WISE to understand GAMA
Abstract: Beyond the Galactic Plane, WISE source counts are dominated by the extragalactic sky: nearby resolved galaxies at the bright end, and a full range of evolving populations to the flux limits of WISE. It is our aim to characterize these populations, constructing a census and ultimately 3-D map of their distribution. Here we report on results focused on the Galactic caps, some 600 sq. degrees, including the GAMA G12 field. We use the full measurements of the WISE point source catalogues, our own measurements of resolved sources, and the deep photo- spectroscopic survey GAMA to understand color combinations, luminosity distributions and spatial clustering.
Title: The SUNBIRD survey: revealing obscured supernovae with Gemini
Abstract: The SUNBIRD (Supernovae UNmasked By InfraRed Detection) project aims to reveal the population of dust-obscured supernovae occurring in Luminous Infrared Galaxies (LIRGs). Such discoveries are vital for determining the fraction of all supernovae which will be missed by current and future optical surveys. LIRGs are the ideal hunting grounds for finding obscured supernova, since these starburst galaxies are expected to host a large number of supernovae as well as contain a lot of dust. With the use of near-infrared observations from GeMS/GSAOI, the laser guide star adaptive optics imager on Gemini South in Chile, in just the first semester we have discovered 2 supernovae, and confirmed 1 found previously. In this talk I present the first results of SUNBIRD and discuss the advantages, and problems, of using a state-of-the-art instrument such as GeMS/GSAOI.
Title: Extremophiles: Living on the edge
Abstract: Are we alone? What are the possibilities for life on other planets in Solar system? How to detect life conditions on extrasolar planets? Are living creatures able to survive in the extreme environments?
Astrobiology is one of the disciplines trying to find the answers on some of these important questions. It’s method is very simple: exploring the organisms living in the extreme environments in our own planet enables us to determine the range of conditions that can support life somewhere else.
In this talk I will introduce the Extremophiles: creatures that thrive in conditions unimaginable to any human being. Creatures that require extreme and often poisonous environments for their growth and reproduction, and die if we expose them to the conditions optimal to humans.
Title: Confronting Uncertainties in Stellar Physics: calibrating overshooting and quantifying theoretical uncertainties
Abstract: In the past decade, the number of stellar evolution codes available has increased dramatically. The outputs of these codes, often freely available, are used in several fields of astrophysics (exoplanets, asteroseismology, stellar populations…) to explain and predict a large variety of observations. Nevertheless, it is not straightforward to directly link observations and theory in a fully consistent manner, properly taking into account the uncertainties, particularly the theoretical ones. As a result, observers often wrongly consider their preferred set of stellar evolution tracks as intrinsically correct. Therefore, we have set up the “Confronting Uncertainties in Stellar Physics” project, the aim of which is to better quantify the impact of theoretical uncertainties in the use of stellar evolution models. In this talk, I will first present an attempt to calibrate convective overshooting in low- to intermediate mass stars by means of eclipsing binary systems. I will then assess the systematic uncertainities in stellar evolutionary calculations for main-sequence stars by comparing stellar tracks from several different evolution codes, and some possible causes of the origin of these uncertainties.
Title:The effects of non-ideal MHD on disc-wind solutions of Protoplanetary Discs
Abstract: Protoplanetary discs are the precursors of planets. These systems are of great interest with the recent discoveries of myriad extrasolar planets. Their physical conditions and kinematics have a major bearing on how planets form, so understanding these disks is vital for building models of planet formation. Many of these disks have jets or disc winds, which have significant effects on their evolution. Current models of these outflows typically ignore non-ideal MHD effects, however these effects are known to operate inside these discs, and are known to affect the structure of these discs through effects such as MRI (Magnetorotational Instability). In this talk, I will present preliminary results of adding non-ideal MHD to self-similar solutions of disc winds.
Title: A homogenised distance catalogue for the Galactic Post-AGB population.
Abstract: Post-AGB (PAGB) stars are the short-lived, low-intermediate mass objects transitioning from the asymptotic giant branch (AGB) to the white dwarf (WD) phase. These objects are characterised by a constant, core-mass dependent luminosity and a large infrared excess caused by the dusty envelope ejected at the top of the AGB. PAGB stars provide us with insights into the evolution of their direct descendants, planetary nebulae (PNe). The calculation of physical characteristics of PAGB are dependent on accurately determined distances, which are scarcely available in the literature. Using the existing Torun catalogue for PAGB objects and supplementing this with archival data, we have determined distances to the entire Galactic population of PAGB stars by modelling their spectral energy distributions (SED) with black bodies and numerically integrating over the entire wavelength range to determine the total integrated flux of the object. For the bulk of the PAGB stars we have assumed the luminosities of these objects based on their positional characteristics and stellar evolution models. The RV Tauri stars however are known to follow a period-luminosity relation (PLR) reminiscent of type-2 Cepheids, so for these variable PAGB stars we have determined their luminosities via the PLR. Here we present the first homogeneously determined catalogue of distances for the entire Galactic population of PAGB stars. This will allow us to overcome the biggest obstacle to uncovering the mystery of these poorly understood objects which play a vital part in the chemical enrichment of the Galaxy.
Title: AGN component in Deep Radio Fields
Abstract: I will present a short update about my PhD project, focusing on the two main topics which I worked on in the last two years: Infared-Faint Radio Sources (IFRS), a recently discovered class of high-redshift AGNs; and Radio-Quiet AGNs (RQ AGN), a new component of the AGN population discovered in very deep surveys. In both cases I will give a short introduction about the current hypotheses on the nature of these objects, and I will present my personal contribution on the topics.
Title: Identifying member and ex-member stars of globular clusters.
Abstract: Globular clusters (GCs) are temporary (although relatively long-lived) residents of the Galaxy and those that exist now are survivors of a much larger population. These remnant GCs are also much smaller now as stars are removed by processes such as tidal or disk shocking as they orbit the Galaxy. Many studies have reported these stellar deserters near clusters as well as among field stars in the Galactic halo etc.
Title: From Planets to Gravitational Waves: Latest Results from Parkes Pulsar Timing
Abstract: Pulsar timing, the careful monitoring of the arrival times of pulses, underpins a wide range of cutting edge science. It is the premier means for probing the nature of neutron stars, it admits precise tests of general relativity, and it promises the detection of low-frequency gravitational waves. I will discuss the latest results from two samples of pulsars my colleagues and I are timing with the Parkes telescope.
The first is a large sample of young pulsars, originally selected to support the Fermi gamma-ray telescope, which we have been timing since 2008. With this long dataset we placed exceedingly stringent limits on the existence of planets around young pulsars, with implications for supernova debris disks. We also identified seven pulsars whose quasi-periodicity may be a hallmark of neutron star precession.
Next, I will discuss the recent activities of the Parkes Pulsar Timing Array, who time an ensemble of millisecond pulsars and who recently published a world-leading upper limit on a gravitational wave background from supermassive black hole mergers. Finally, I will briefly describe the groundbreaking ultra-wideband receiver being developed for Parkes; its capabilities will be instrumental in keeping Parkes at the forefront of the field.
Title: Magnetic fields in star and planet formation
Abstract: In this talk I shall review the role played by magnetic fields during the formation of stars and planetary systems. Magnetic fields remove angular momentum during the collapse of molecular cloud cores, determining the initial mass and size of protoplanetary discs. The discs’ subsequent evolution as planets are formed is complex, with magnetic fields determining the extent of the turbulent gas motions that control the agglomeration of solids that begins the process of planet building. Magnetic fields also affect the speed and direction of migration of protoplanetary cores and planets.
Progress has been severely hampered by the lack of empirical constraints on disc models, particularly on the magnetic field strength and geometry. I conclude by discussing prospects for improving this situation using the capabilities offered by ALMA.
Title: The Milky Way disk
Abstract: I am going to touch those topics that can be considered hot nowadays in the Galactic disk research: the reality of the thick disk, the spiral structure of the Milky Way, and the properties of the outer Galactic disk. A lot of work has been done in recent years on these topics, but a coherent and clear picture is still missing. Detailed studies with high quality spectroscopic data seem to support a dual Galactic disk, with a clear separation into a thin and a thick component. Much confusion and very discrepant ideas still exist concerning the spiral structure of the Milky Way. Our location in the disk makes it impossible to observe it, and we can only infer it. This process of inference is still far from being mature, and depends a lot on the selected tracers, the adopted models and their limitations, which in many cases are neither properly accounted for, nor pondered enough. Finally, there are very different opinions on the size (scale length, truncation radius) of the Galactic disk, and on the interpretation of the observed outer disk stellar populations in terms either of external entities (Monoceros, Triangulus-Andromeda, Canis Major), or as manifestations of genuine disk properties (e.g., warp and flare).
Title: Hydrodynamics of the common envelope phase in binary stars
Abstract: The common envelope (CE) phase is an important stage in binary stellar evolution. It is needed to explain many close binary stellar systems, such as cataclysmic variables, Type Ia supernovae, or X-ray binaries: to form the resulting close binary, the initial orbit has to shrink, thereby transferring energy to the primary giant’s envelope that is hence ejected. The details of this interaction, however, are still not understood.
Here, I present new hydrodynamic simulations of the dynamical spiral-in forming a CE system using the moving-mesh code AREPO. The nearly Lagrangian scheme combines advantages of smoothed particle hydrodynamics and traditional grid-based hydrodynamic codes and allows us to capture also small flow features at high spatial resolution. About 20 orbits after the in-spiral, a new phenomenon is observed: large-scale flow instabilities are triggered by shear flows between adjacent shock layers. These indicate the onset of turbulent convection in the common envelope, thus altering the transport of energy on longer time scales.
Title: Modeling Type Ia supernovae
Abstract: Type Ia supernovae play an important role in observational cosmology and in various astrophysical processes. However, the question of the progenitor systems from which these cosmic explosions arise and of their physical mechanism are not settled yet. Several possibilities have been suggested and after introducing some general concepts of thermonuclear astrophysical explosions I will discuss recent developments by presenting multidimensional simulations that refer to different scenarios. In combination with detailed radiative transfer calculations that predict observables from the models and comparison with astronomical data, these shed light on the progenitor systems.
Title: In Search of Lost Shocks
Abstract: State of the art three dimensional magnetohydrodynamic (MHD) simulations have shown that the character of star formation is sensitive to the details of supersonic turbulence within giant molecular clouds. A significant amount of the turbulent energy dissipates in shock waves, and so the radiative signatures of shocks probe the turbulence. In this talk, I highlight the importance of accounting for the different families of MHD shocks, and summarise my efforts to find such shocks in a high resolution simulation of molecular cloud turbulence.
Title: A Tale of Two Shells (Or: Adventures in Blobology)
Abstract: Dense, star-forming gas is thought to form at the stagnation points of large-scale interstellar medium flows, but observational examples of this process in action are rare. I will present an unusual example of a Giant Molecular Cloud (GMC) sandwiched between two colliding Milky Way supershells, which shows strong evidence of having formed from material accumulated at the collision zone. I will compare the usual observational suspects (12CO, 13CO, and C18O(J=1-0) molecular line data) with high-resolution hydrodynamical simulations of colliding stellar-wind bubbles, to argue that the cloud was partially seeded by pre-existing denser material, but assembled into its current form by the action of the shells. This assembly includes the production of some new molecular gas. The location of the GMC at the interface of two shells may support recent theoretical work which emphasises the importance of multiple episodes of compression to overcome magnetic support.
Title: Molecular filament formation in the ISM
Abstract: In this talk I will present two different research projects, both related to the formation of interstellar molecular filaments.
In the first part of my talk I will talk about simulations of superbubbles. In this project we show how the combined feedback of supernova explosions and stellar winds from associations of massive stars can trigger the formation of molecular clouds. In particular, we explore the effects of self-gravity and magnetic fields on the structure of two shells as they expand and collide in a turbulent diffuse medium. Our main finding is that for the conversion of warm to cold ISM gravity plays a minor role, but magnetic fields completely alter the expansion behavior of the superbubble, as well as the morphology of the dense gas formed on the shells.
In the second part I will present some theoretical work aimed to explain the apparently universal thickness of molecular filaments as observed with Herschel. Their width is found to be 0.1 pc over a very wide range of column densities, which poses a challenge on theoretical models of ISM turbulence. The theory we propose is that ambipolar diffusion could be setting that scale. To test this theory we perform 3D simulations of ideal and non-ideal MHD turbulence and study the effect of ion-neutral friction on the formation of dense filaments in a molecular cloud. We find that when ambipolar diffusion is included, both driven and decaying turbulence show a significant change in the number of filaments formed and in the filament appearance. Our main conclusion is that non-ideal MHD effects are essential in the study of ISM turbulence and that ambipolar diffusion in particular is a very good candidate for setting the characteristic 0.1 pc scale of molecular filaments.
Title: A heuristic approach to fitting dusty disks about asymptotic giant branch stars.
Abstract: Circumstellar disks are believed to play an important role during the final stages of evolution of small to medium mass stars, a phase in which theory does not yet explain observations entirely.
We set out to constrain disk parameters, of which little is known, in the hope of better understanding possible evolutionary paths. We apply numerous genetic algorithms to the fitting of radiative transfer models to interferometric observational data. By doing so, we are able to derive relative likelihood functions for the input parameters, an ability that allows us to better constrain a disk's structure and to ultimately gain understanding in this complex phase of stellar evolution.